1. Field of the Invention
This invention relates to an apparatus for producing electrolytic ionized water (hereinafter referred to as EIW) which is applicable to sterlization, anti-oxidation treatment for metal surfaces, and washing and removing various contaminants sticking onto surfaces of solid objects and so on.
2. Description of the Related Art
In the following description, the term "anode" denotes an electrode to which a positive voltage is applied in an electrolyzer performing electrolysis by conducting a direct current to a water or aqueous solution. Likewise, the term "cathode" denotes an electrode to which a negative voltage is applied. During the electrolysis, an aqueous solution present around the anode is called "anode chamber EIW", while an aqueous solution around the cathode is called "cathode chamber EIW".
Positive charges are applied to the anode while negative charges are applied to the cathode. Specifically, the anode functions to take electrons away from the anode chamber water, while the cathode functions to provide the electrons to the cathode chamber water.
The water or aqueous solutions which are obtained through the electrolysis are generally called EIW. Further, the term "electrolysis" denotes simply to apply a DC voltage to a water or aqueous solution, but it is not necessary confined to such a process in which a direct current is conducted following the application of the DC voltage to effect electrolytic reactions thereby, decomposing the water or aqueous solution into oxygen and hydrogen. When an anode chamber and a cathode chamber are separated in an electrolyzer by a diaphragm made of a synthetic polymer (e.g. polyethylene, polypropylene, polyester, polystyrene, fluororesin and so forth) or an inorganic substance such as ceramics, the anode is housed in the anode chamber while the cathode is housed in the cathode chamber.
Generally speaking, the anode chamber water is oxidative, and has a high oxidation-reduction potential while the cathode chamber water is reductive, and has a low oxidation-reduction potential. In addition to the oxidation and reduction characteristics of the chamber EIW, when influent water to an electrolyzer contains electrolytes, the anode chamber effluent generally has an acidic hydrogen ion activity (pH) while the cathode chamber effluent has an alkali hydrogen ion activity (pH).
The anode chamber effluent has the oxidation characteristics because oxygen, ozone and other products oxidized from other matter are generated on a surface of the anode. With respect to the cathode chamber effluent, hydrogen and other products reduced from other matter are generated.
The anode chamber effluent has the acidic pH because anions are attracted to the positive charges of the anode, and cations are driven away from the anode, so a hydrogen ion anode chamber EIW has an acidic pH whereas the cathode chamber EIW has an alkaline pH. The reason why the anode chamber EIW is oxidative is that oxidative products are present on the surface of the anode, which products include oxygen and ozone generated on the anode surfaces and other oxidative substances formed by the oxidation on the surfaces of the anode. On the other hand, the reason why the cathode chamber EIW is reductive is that reductive products are present on the surfaces of the cathode, which products include hydrogen generated on the cathode surfaces and other reductive substances formed by the reduction on the surfaces of the cathode.
The anode chamber EIW produced by the electrolysis has strong sterilization characteristics because of its oxidative nature, and has been widely used as sterilizing water in hospitals, dental clinics, restaurants, food processing industries, and so on. The cathode chamber EIW is known to be effective in preventing metal surfaces from being oxidized by oxygen in the atmosphere in metal parts manufacturing processes, and so on. Further, the foregoing anode and cathode EIW are known to be effectively used to wash off various contaminants sticking to surfaces of solid objects.
Various contaminants such as metals, particles, oil and the like on the solid objects can be effectively cleaned using cleaning solutions whose oxidation-reduction potential and pH are adjusted to the conditions of the surfaces of the objects to be cleaned. For instance, an acidic and oxidizing cleaning agent is effective in ionizing, dissolving and removing metallic impurities from a solid object. Further, organic contaminants such as oil can be effectively oxidized, decomposed and removed using oxidizing cleaning solutions.
Most of particulate substances are usually charged opposite to the charge of a surface of a solid object and are electrostatically attracted thereto. An alkaline and reducing cleaning solution can often alleviate the electrostatic attraction of the particles to the solid object, suspend and float them therein, and remove them off from the surface of the solid object.
FIGS. 2 and 3 of the accompanying drawings show examples of EIW producing apparatuses of the prior art. Specifically, the apparatus of FIG. 2 includes an electrolyzer 101 having two electrolytic chambers, while the apparatus of FIG. 3 includes an electrolyzer 201 having three electrolytic chambers.
Referring to FIG. 2, the electrolyzer 101 has an anode chamber 106 and a cathode chamber 108 which are partitioned by a diaphragm 102. The anode chamber 106 houses an anode 104, while the cathode chamber 108 houses a cathode 105. Each of these chambers 106 and 108 receives influent water via an inlet line 109. Two water electrolyzed in these chambers 106 and 108 flow out therefrom via outlet lines 114 and 116, respectively. A DC voltage is applied to the anode 104 and the cathode 105 via power supply lines 118 and 119, respectively.
The electrolyzer 201 in FIG. 3 has an anode chamber 206, an intermediate chamber 207 and a cathode chamber 208. The intermediate chamber 207 is sandwiched between the anode chamber 206 and the cathode chamber 208, and is partitioned from these chambers by diaphragms 202 and 203. Influent water such as tap water, deionized water or the like is supplied to these chambers 206, 207 and 208 via an inlet line 209. From these chambers, three kinds of EIW flow out via outlet lines 214, 215 and 216. Reference numerals 218 and 219 denote power supply lines for applying a DC voltage to the anode 204 and the cathode 205, respectively.
The conventional apparatuses shown in FIGS. 2 and 3 have the following drawbacks when they are used to produce EIW which is used to prevent oxidation of metal surfaces, for the cleaning of solid objects carrying various contaminants thereon, and so on.
For instance, in the electrolyzer of FIG. 2, the anode chamber 106 and the cathode chamber 108 are simply separated by the diaphragm 102 made, for example, of a porous polymeric membrane. Thus, a part of oxidizing substances formed on the anode and a part of reducing substances formed on the cathode may inevitably migrate into the adjacent chambers 108 and 106 via the diaphragm 102, respectively. Thus, a part of the useful oxidizing substances or reducing substances may be made to disappear due to oxidation-reduction reaction of the oxidizing and reducing substances. This means reduced efficiency of the production of EIW. Further, it is difficult to selectively determine characteristics of EIW such as a wide range of oxidation-reduction potentials, pH's and so on.
In contrast, the 3-chamber type electrolyzer can overcome the foregoing drawback, i.e. a part of the useful oxidizing substances or a part of the reducing substances can be prevented from migrating into the adjacent chamber because of the presence of the intermediate chamber to which the influent water is supplied. However, this apparatus also has difficulty in selectively determining characteristics of EIW such as a wide range of oxidation-reduction potentials, pH and so on. For instance, when deionized water is electrolyzed, the resultant anode chamber water and cathode chamber water have oxidation-reduction potentials and pH's in very limited ranges. Further, even if deionized water added with an electrolyte is used, it is very difficult to selectively and arbitrarily determine the oxidation-reduction potentials and pH's of the anode chamber EIW and the cathode chamber water as desired.
This problem is serious when EIW is used for cleaning purposes.
In order to enhance cleaning effects on an industrial scale, it is necessary adequately, to examine materials treatment of the surfaces of the objects to be cleaned, and the nature and condition of contaminants adhering to the objects, and to select those characteristics of cleaning solutions such as oxidation-reduction potential, pH and so on which are best suited for objects to be cleaned. Further, contaminants of solid objects are usually a mixture of metals, particulate substances, oil and the like. In such a case, a plurality of cleaning solutions should be sequentially used in combination so as to accomplish cleaning results as desired. For this purpose, it is preferable that the characteristics, i.e. the oxidation-reduction potential, pH and the like, of the anode chamber and the cathode chamber EIW can be independently and selectively determined in desired ranges. However, the foregoing 3-chamber type electrolyzer apparatus cannot meet this requirement, i.e. it is not possible independently to determine the characteristics of the water emerging from each chamber. When operating conditions such as the amount of electrolytes to be supplied, and the composition, concentration or pH of EIW after the addition of electrolytes to the the influent water to be subjected to the electrolysis are determined on the basis of the desired characteristics of the anode chamber EIW to be used for the cleaning, the characteristics of the cathode chamber EIW, which is simultaneously produced with the anode chamber EIW, inevitably depend upon those operating conditions for producing the anode EIW desired. Thus, it is very difficult to independently and selectively determine the characteristics of the cathode chamber EIW useful for the cleaning. The same is true of a case in which the characteristics of the cathode chamber water are used as criteria. Therefore, it is substantially impossible to effectively produce the anode chamber EIW and the cathode chamber water both having desired characteristics by use of either of the apparatus shown in FIGS. 2 and 3. This is because the operating conditions for producing the desired anode chamber EIW are different form those for producing the desired cathode chamber water. The foregoing problem is an obstacle to the application of the electrolyzed water producing apparatus on an industrial scale.
There are additional problems in the EIW producing apparatuses shown in FIGS. 2 and 3. Specifically, one is that electrolytes for the cleaning solution have to be wasted, and the other is that cleaning solutions suitable for assuring highly clean objects is difficult to obtain, as described below.
In order to simultaneously produce both the acidic and oxidizing anode chamber EIW and the alkaline and reducing cathode chamber EIW in one apparatus, it is necessary to use aqueous solutions of salt, as the influent water, which consists of cations other than hydrogen ions and anions other than hydroxide ions, to make the anode chamber water and the cathode chamber EIW acidic and alkaline, by migrating the electrolyte ions in electrolytic chambers. However, when such influent water is used, a relatively large amount of cations other than the hydrogen ions which are contained in the influent water would inevitably remain in the anode chamber EIW produced. Similarly, a relatively large amount of anions other than the hydroxide ions would inevitably remain in the cathode chamber water. Therefore, in order to set the pH of the anode chamber water at a target value, anions other than the hydroxide ions are required so as to neutralize the remaining cations and to attain the target pH. As for the cathode chamber water, additional cations other than the hydrogen ions are necessary so as to neutralize the remaining anions and to attain the target pH. This means that a considerable amount of chemicals are necessary to neutralize the ions. Such chemicals are not indispensable to the original functions of the EIW producing apparatuses.
In the case of electronic devices which should be extremely clean, the presence of impurities in cleaning solutions seriously affects the characteristics and yield of the electronic devices. Thus, the cleaning solutions should be substantially free from any impurities. However, if the anode chamber EIW contains residual cations original with the influent water other than the hydrogen ions, or if the cathode chamber EIW contains the residual anions original with the influent other than the hydroxide ions, such residual ions become impurities, and tend to be deposited on the surfaces of the electronic devices as solid salts or ionic crystals, when the electronic devices are dried. Deposition of such solid salts would adversely affect the characteristics and yield of the electronic devices.
At present, the deposition of the above-mentioned ionic crystals on the electronic devices is evaded by using cleaning solutions in which alkali such as ammonia or acid such as hydrochloric acid or sulfuric acid, and hydroperoxide are mixed at certain ratios. In this case, the cleaning solutions are diluted with high-purity water.
When EIW (i.e. anode chamber EIW water and cathode chamber EIW) produced by the apparatus shown in FIGS. 2 or 3 for which electrolyte influent water is fed, are used to clean the electronic devices in place of the above-mentioned cleaning solutions, it is still impossible to overcome the problem that the deposition of the ionic crystals on the dried electronic devices adversely and seriously affects the characteristics and yield of the electronic devices.
Granted that all of the foregoing problems are overcome, it is very difficult to produce, on a commercial scale, the electrolyzed water without impurities as long as electrolyte influent water is used for the apparatus of FIGS. 2 or 3. This is because impurities tend to be mixed during the production of electrolytic solution from the influent.
When an electrolyte water solution is used as the influent water for the electrolyzed water producing apparatus, the influent is required to be substantially free from impurities. In order to prepared such influent water the influent, it is conceivable to add highly pure electrolyte to deionized water or high-purity water. Chemicals (electrolytes) which are pure enough to be used for cleaning the electronic devices and are available on an industrial scale are mainly aqueous solutions of acids and bases. However, to simultaneously produce acidic and oxidizing anode chamber EIW and alkaline reducing cathode chamber water using the apparatus of FIGS. 2 or 3, it is required that cations other than the hydrogen ions and anions other than the hydroxide ions should coexist in the influent water. Thus, an aqueous acid solution and an aqueous basic solution have to be mixed at a predetermined ratio. For this purpose, a facility for mixing such solutions is necessary. This not only complicates the EIW producing process but also causes problem that the electrolyte water solution may be contaminated during the mixing process.